This type of rotation angle detection device is disclosed in the following Patent Documents 1 and 2. The rotation angle detection device disclosed in Patent Document 1 includes a magnet which is annularly formed, and into which a shaft is inserted, and magnetic sensors (detection elements) which are disposed on the axial lines extending orthogonally to each other from the rotation center of the shaft along the rotation surface of the magnet. The angle detection device disclosed in Patent Document 2 includes a rotation member which is annularly formed, and into which a shaft is inserted; a magnetic plate which is disposed faced to the outer peripheral surface of the rotation member; and detection elements which are disposed on the axial lines extending orthogonally to each other on the magnetic plate in an axial direction and a radial direction of the shaft. With these devices, the rotation angle of the shaft which is rotated integrally with the magnet and the rotation member is identified on the basis of a change in magnetism which has been detected by the respective detection elements. Specifically, the rotation angle is detected on the basis of the ratio between the magnetic flux densities which have been detected by the detection elements disposed on the axial lines (X-axis and Y-axis). This detection result is outputted after having been transformed so as to provide a linear change in proportion to the rotation angle.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-263585
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2008-292466